An apparatus and method are provided for allowing UPnP devices to exchange power mode information with one another in a unified home network. The method of relaying a message in a unified network including at least first and second networks, the method includes receiving information regarding a power mode of a communication device connected to the first network from the communication device, generating a message indicating the power mode of the communication device based on the received information, and transmitting the message to the second network so that communication devices connected to the second network recognize the power mode of the communication device connected to the first network. Accordingly, even if a UPnP device in the power save mode cannot receive or transmit messages, another UPnP device can determine whether the UPnP device is connected to a network. If a new UPnP device generates an IP address according to an automatic IP mechanism, it is possible to prevent IP collision caused by a UPnP device that is connected to an IP network but operating in the power save mode.